Chapter 4 Assessment Key: 83, 85-89, 106
83. Write the symbols used to denote alpha, beta, and gamma radiation and give their mass and
charge.
Mass
(amu)
Charge
He
4
2
beta

1/1840
1
gamma

0
0
Particle
Symbol
4
2
alpha
85. Radioactive Emissions What change in mass number occurs when a radioactive atom
emits an alpha particle? A beta particle? A gamma particle?
, mass number decreases by 4; , no change in mass number; , no change in mass
number
86. What is the primary factor determining whether a nucleus is stable or unstable?
the neutron-to-proton ratio
87. Explain how energy loss and nuclear stability are related to radioactive decay.
Radioactivity results when unstable nuclei emit energy in order to gain stability.
88. Explain what must occur before a radioactive atom ceases to undergo further radioactive
decay.
A stable, nonradioactive atom must be formed.
89. Boron-10 emits alpha particles and cesium-137 emits beta particles. Write balanced nuclear
reactions for each radioactive decay.
10
5
B  63 Li  42 He
137
55
Cs 
137
56
Ba 
0
1
e
106. Magnesium constitutes about 2% of Earth’s crust and has 3 naturally occurring isotopes.
Suppose you analyze a mineral and determine that it contains the three isotopes in the
following proportions Mg-24 (abundance  79%), Mg-25 (abundance  10%), and Mg-26
(abundance  11%). If your friend analyzes a different mineral containing magnesium, do
you expect him to obtain the same relative abundance of magnesium? Explain.
Yes. The isotopic abundance of an element is the same no matter where the element
comes from.